If you really have the patience, i'd try building the wheels yourself. The one off cost of buying all the necessary tools and stands to do this however is going to be a lot (you forgot a tensionmeter). It will also take you a long time to build those wheels purely because you've never done it before.

If you want to save some money, Tiagra will work just as well as 105, just not as blingy.

Budget wise, you'd be better off buying a bike complete than buying these components seperately. This is much more expensive unless you are hunting for deals on every component (which may also take a long time).